Electrical and thermal transport properties of intermediate-valence YbAl3

Abstract

Intermediate valence compound YbAl3 has been synthesized by the Bridgman method. Temperature dependence of the Seebeck coefficient, electrical resistivity and thermal conductivity has been measured on YbAl3 hot-pressed and single crystal samples. At temperatures below 100 K, the electrical resistivity exhibits a ρ(T) = ρ0 + AT2 dependence, while over the temperature range 300-800 K YbAl3 exhibits metallic behaviour with a linear temperature dependence of the electrical resistivity. The Seebeck coefficient exhibits a temperature dependence typical for heavy fermion compounds and attains a maximum of its absolute value of -79 µV K-1 at around 200-250 K. Combination of a large Seebeck coefficient and low residual resistivity of single crystalline YbAl3 leads to the highest ever reported electrical power factor of 340×10-6 W cm-1 K-2 at 80 K. Thermal conductivity as a function of temperature has a broad peak at 50 K, which originated mainly from the electronic contribution to thermal conductivity. At 300 K the total thermal conductivity of hot-pressed samples ranges from 0.085 to 0.179 W cm-1 K-1 depending on the density of the samples. The calculated figure of merit value attains its maximum of 1×10-3 K-1 at 100-120 K.

Achieving high power factor and output power density in p-type half-Heuslers Nb 1-x Ti x FeSb

“…Such an unusually high power factor has previously been observed only in metallic systems such as YbAl 3 and constantan (26,27). Furthermore, a record output power density of ∼22 W·cm −2 with a leg length ∼2 mm is experimentally obtained with T C = 293 K and T H = 868 K. We also observe that the lattice thermal conductivity hardly changes within the range of grain sizes studied in this work.…”

Thermoelectric Power of the URu1-xPdxGe System

“…S(T ) of these compositions is negative over the whole temperature range measured, and do exhibit only one extremum, i.e., a broad minimum around 200 K. This observation hints at a common nature of the phenomena in these alloys. There is a similarity of the data to those previous reported for Yb-based compounds, such as YbAl 3 [13] and YbCu 2 Si 2 [14]. According to the theory [8,9] the minimum can be ascribed to the Kondo scattering on the full CEF split multiplet of the magnetic uranium ions.…”

Optical and transport properties of heavy fermions: theory compared to experiment

“…The resultant ρ(T ) is shown in figure 4 out to T = 800K; and we note that it continues to increase monotonically above 300K, precluding as such the occurrence of a coherence maximum at a T in excess of that shown in figure 3. Experimental results for ρ(T ) up to T ≃ 750K have in fact been reported [34]. This data does not appear to be quite as clean as that of [28] in the interval 50K T < 300K, but for T 50K the ρ(T ) from [34] collapses very well onto that of [28] (considered above) with an overall ρ-axis rescaling factor a = 1.2 (equation (2.1)).…”